Comprehensive UV/vis and Infrared Studies of Light-induced Carbon Monoxide Release From Ruthenium(II) Complexes

The use of carbon monoxide as a therapeutic agent has been demonstrated in pre-clinical trials, with CO-releasing molecules (CORMs) exhibiting anti-inflammatory, anti-proliferative, anti-apoptotic, anti-oxidative and vasodilatory effects. Organometallic compounds that can release CO in a highly controlled fashion under physiological conditions have therefore become a major field of scientific and medical research. Light-induced activation of CORMs is a controlled CO release approach that has received considerable attention. However, despite the number of photo-CORMs reported in the literature, their utility has been limited because excitation into the UV region results in low tissue penetrability and direct damage to healthy tissue. The challenge to extend the excitation wavelength further into the visible region of the electromagnetic spectrum has led us to explore the application of ruthenium(II) -carbonyl complexes as photo-CORMs.
Herein, we report the synthesis of ruthenium(II)-carbonyl complexes (Figure 1) functionalized with bidentate polypyridyl ligands and investigate the mechanism of CO release (before and after light-activation) using a combination of spectral techniques (UV/Vis, FTIR and Raman spectroscopy). The photo-induced CO-release kinetics of the Ru(II)-photo-CORMs, as well as the identity of the intermediates and photo-activated products, will be presented. These results have important implications in guiding the design of new photo-CORMs activated by visible light.